聯立二元一次方程

1.{3x+y=4---------------(1)
{2x+y=6---------------(2)
(1)-(2)
x=-2
sub x=-2 into(2)
-4+y=6
y=10
C
2. {3x+y=4---------(1)
{2x-3y=-1-------(2)
(1)*3
9x+3y=12-----------(3)
(3)+(2)
11x=11
x=1
sub x=1 into(1)
3+y=4
y=1
A
3. {x-3y=6---------(1)
{2x+y=5---------(2)
(1)*2
2x-6y=12-----------(3)
(3)-(2)
-7y=7
y=-1
sub y=-1 into(1)
x+3=6
x=3
B

1. {3x+y=4......(a)
{2x+y=6......(b)
代入法 In (a)
y=4-3x
sub y=4-3x into (b)
2x+4-3x=6
-x=2
x=-2
sub x = -2 into (b)
-4+y=6
y=10
加減消元法
(a)-(b)
3x+y-2x-y=4-6
x=-2
sub x = -2 into (b)
-4+y=6
y=10
ans is c
2. {3x+y=4.....(a)
{2x-3y=-1......(b)
代入法 In (a)
y=4-3x
sub y=4-3x into (b)
2x-3(4-3x)=-1
2x-12+9x=-1
11x=11
x=1
sub x=1 into (b)
2-3y= -1
-3y=-3
y=1
加減消元法 2(a)-3(b)
6x+2y-6x+9y=8-(-3)
11y=11
y=1
sub y=1 into (b)
2x-3=-1
2x=2
x=1

ANS is A
3. {x-3y=6......(a)
{2x+y=5.....(b)
代入法 In (a)
x=6+3y
sub x=6+3y into (b)
2(6+3y) +y=5
12+6y+y=5
7y= -7
y= -1
sub y= -1 into (b)
2x-1=5
2x=6
x=3
sub x=3 into (b)
6+y=5
y= -1
加減消元法 2(a)-b
2x-6y-2x-y=12-5
-7y=7
y=-1
sub y= -1 into (b)
2x-1=5
2x=6
x=3
ANS is B

ANS1.C
ANS2.A
ANS3.B